RAMAN SCATTERING IN V3Si, V3Ge, Nb3Sb, AND Cr3Si : CORRELATION OF Eg OPTICAL PHONON LINEWIDTH WITH MAGNETIC SUSCEPTIBILITY

Abstract

Raman scattering measurements of the Eg optical phonon in V3Si and Nb3Sn show it to have an anomalous width, temperature dependence, and asymmetric lineshape. We have observed a similar, although weaker, anomaly in V3Ge. The Eg and T2g phonons in Nb3Sb and the T2g phonon in Cr3Si show no anomalous behavior and can be understood in terms of simple anharmonic interactions. In Cr3Si the Eg phonon has an anomalous width, shape, and temperature dependence (similar to V3Ge) in spite of its low electronic density of states and temperature independent magnetic susceptibility. A linear correlation is shown to exist between magnetic susceptibility and Eg mode linewidth, Ɖ, in V3Si, Nb3Sn, and V3Ge. With the aid of a simple model, most of the features of the Raman data can be understood in terms of direct coupling of the E phonon to interband electronic transitions between the very flat bands emanating from the Ɖ12 level in these compounds. These results indicate that direct coupling of the Eg optical phonon to the Ɖ12 bands plays a major role in the splitting of the cubic Ɖ12 subband N(E) peak by the dimerization of the transition metal sublattice.